1. Field of the Invention
The present invention relates to a liquid crystal display device capable of providing color display and, more particularly, to a liquid crystal display device using novel color filters which are improved in the efficiency of utilization of light.
2. Description of the Related Art
Liquid crystal display devices are widely used as high-resolution display terminals for notebook type computers and computer monitors. Liquid crystal display devices are remarkable in technological advance, and have been able to provide display qualities which are close to those of CRTs. However, the liquid crystal display devices have not yet been satisfactory in terms of kinetic image display, color reproducibility and brightness, and also have the problem that a further reduction in manufacturing cost is needed.
The liquid crystal display devices are classified into a simple matrix type in which multiple pairs of electrodes which intersect each other are formed on the inner surfaces of a pair of substrates and pixels are formed at the respective intersection positions, and an active matrix type in which each pixel has a switching element. In particular, the active matrix type of liquid crystal display device is classified into a so-called vertical electric field type (TN type) and a so-called in-plane switching type (IPS type) in accordance with liquid crystal driving mode thereof.
The vertical electric field type of liquid crystal display device includes transparent substrates which are disposed in opposition to each other with a layer of liquid crystal compounds (hereinafter referred to simply also as a liquid crystal layer) being interposed therebetween, pixel electrodes made of transparent electrodes which are respectively disposed in regions corresponding to unit pixels on the liquid-crystal-side surface of either one of the transparent substrates, and counter electrodes made of transparent electrodes which are respectively disposed in the regions on the liquid-crystal-side surface of the other of the transparent substrates. The vertical electric field type of liquid crystal display device is constructed to visibly display an image or the like by modulating light which passes through the liquid crystal layer, by means of electric fields generated between the pixel electrodes and the counter electrodes perpendicularly to the transparent electrodes.
The in-plane-switching type of liquid crystal display device includes transparent substrates which are disposed in opposition to each other with a liquid crystal layer being interposed therebetween, and pixel electrodes and counter electrodes which are disposed on either or both of the liquid-crystal-side surfaces of the respective transparent substrates in such a manner that a pixel electrode and a counter electrode are disposed in each region corresponding to a unit pixel. The in-plane-switching type of liquid crystal display device is constructed to visibly display an image or the like by modulating light which passes through the liquid crystal layer, by means of electric field components generated between the pixel electrodes and the counter electrodes approximately in parallel with the transparent electrodes.
Unlike the vertical electric field type of liquid crystal display device, the in-plane-switching type of liquid crystal display device is known as a device which is superior in so-called viewing angle characteristic, because a user can view a clear image or the like even when the user observes the display surface at a large viewing angle relative thereto.
FIG. 25 is a diagrammatic cross-sectional view for schematically explaining electric fields for pixel formation in an in-plane-switching type of liquid crystal display device. FIG. 26 is a plan view for schematically explaining the construction of one pixel and the vicinity thereof on the lower substrate shown in FIG. 25.
This liquid crystal display device has video signal lines (drain lines) DL, counter electrodes (common electrodes) CT and pixel electrodes PX all of which are formed on one substrate SUB1 which constitutes the lower substrate. The liquid crystal display device also has a protective film PSV deposited to overlie these electrodes DL, CT and PX, and a lower alignment control layer (lower alignment film) ORI1 at the interface between the protective film PSV and a liquid crystal LC. A gate insulating layer GI is provided for covering scanning lines or scanning electrodes (gate lines or gate electrodes) GL.
Each of the video signal lines DL is made of two metal layers d1 and D2, and each of the counter electrodes CT is composed of a metal layer g1 and a protective layer AOF formed to cover the metal layer g1.
A plurality of color filters FIL (in this example, color filters for three colors) partitioned by a black matrix BM are formed on a substrate SUB2 which constitutes an upper substrate, and an overcoat layer OC is formed to cover these color filters FIL. This overcoat layer OC has the function of prevent the constituent material of the color filters FIL or the black matrix BM from penetrating the liquid crystal LC and affecting the characteristics of the liquid crystal LC, as well as the function of leveling the surfaces of the respective color filters FIL. An upper alignment control layer (upper alignment film) ORI2 is formed at the interface between the overcoat layer OC and the liquid crystal LC.
Upper and lower polarizers POL1 and POL2 are stacked on the outer surfaces of the upper and lower substrates SUB1 and SUB2, respectively.
As shown in FIG. 26, a thin film transistor TFT uses a gate line GL as its gate electrode, and has a source electrode SD1 and a drain electrode SD2 which extends from a drain line DL. The source electrode SD1 and the drain electrode SD2 are formed over the gate line GL with a semiconductor layer AS being interposed therebetween, and common electrodes CT extend from a common electrode CT in such a manner as to be disposed adjacent to a pixel electrode PX.
In general, in the related-art liquid crystal display device, a color filter layer composed of three kinds of color filters each of which passes therethrough only a specific wavelength range of light illuminating the display device is used as means for colorizing images. This color filter layer is intended to realize a full color display by dividing a pixel corresponding to one dot of a color display into three unit pixels and disposing filters which respectively correspond to red (R), green (G) and blue (B) in each of the unit pixels as the three primary colors (display primary).